A team of researchers has discovered that the sounds emitted by the tags may aid predators in finding the fish. The tags, which are commonly used in mark-and-recapture studies which inform us on fish survival and stock levels, send out an ultrasonic ping which is supposed to alert scientists to the location of the fish. As it turns out, it may well be alerting other animals to their presence too.

tagging fish

The tagging fish experiment

A team from the University of St. Andrews, Scotland, built a maze of 20 boxes, two of which contained fish. One set of fish was tagged, the other untagged. Grey seals were put into the maze to act as predators.

The study reveals that over the course of 20 trials, 10 grey seals were much quicker to find the tagged fish. They also went to the box full of tagged fish more often than any other box, which would suggest that they were zeroing in on the scientific equipment.

“The seals found the tagged fish sooner and with less searching than the fish without a tag,” says Amanda Stansbury of the Sea Mammal Research Unit at St. Andrews. “This means that the seals learned to use the sound from the pinging tags to find where their food was hidden. This tells us that seals can exploit new sounds, such as fish tags, and use them to their advantage.”

Tagging fish: Detrimental to stocks and science

As well as helping predators to deplete the very fish stocks that the tags are supposed to protect, the scientists are concerned that tagging may have an adverse impact on the accuracy of marine research.

“We expect that other marine mammals are similarly able to use such information to find prey,” says Stansbury. “Tagged fish may be more detectable by predators, which could affect the results of fish studies.”

The paper was published in the journal Proceedings of the Royal Society B.